The present process relates to an isotopic enrichment process, and an apparatus, where light from a laser is used to excite a compound of one isotope of an element, present as a mixture of isotopic compounds, with reaction of the excited compound with a gaseous scavenger effected to remove that isotope, while the compounds of the other isotopes remain stable, and separation of the reaction product, formed with the gaseous scavenger, provides for separation of the one isotope from the other isotopes.
The separation of, or enrichment of, an isotope of an element relative to other isotopes of the element is desired where one isotope possesses certain properties that are not possessed by other isotopes of the element. In the case of zirconium, for example, naturally occurring zirconium contains a mixture of zirconium isotopes; zirconium 90, zirconium 91, zirconium 92, zirconium 94, and zirconium 96. In the use of zirconium in cladding for nuclear fuel rods the zirconium 90 isotope has a lower capture cross-section for thermal neutrons. It is thus desired to form such cladding from zirconium which has a high zirconium 90 isotope content, higher than the 51.5 percent content of zirconium 90 present in naturally occurring zirconium.
The isotopic enrichment of elements by the use of laser techniques is known. Such techniques generally use lasers in conjunction with a carrier gas to transport and cool a compound of an element to be enriched. Such a process, however, has many practical and economic difficulties. For example, a compound containing the element to be enriched must have a high vapor pressure and, furthermore, the compound must be produced at a reasonable cost. Also, due to nucleation problems induced when the carrier gas is cooled in a supersonic nozzle, the concentration of the element to be enriched must be kept very low. It follows, then that very large compressors are required for handling the carrier gas, resulting in high capital and operating costs. In addition, the low concentration of active element makes it very difficult to use a significant portion of the laser beam due to the nozzle manufacturing difficulties and losses in mirrors and windows. In addition to the above difficulties, the use of a scavenger-type reaction where the isotope of interest is selectively excited and reacted with a scavenger gas is all but ruled out because the gas is cooled in a supersonic nozzle. Thus, the outlet gas has very few molecular collisions and the likelihood of a scavenger-excited molecule collision is very low.
As examples of recent laser-induced isotope separation processes, U.S. Pat. No. 4,032,419 teaches a process to separate U-235 from U-238 in a compound, where the compound is irradiated, in crystalline form of the solid phase, at a first frequency to excite the U-235 but not the U-238. The compound is then irradiated, in crystalline form of the solid phase with a second frequency to dissociate or ionize the U-235, and the irradiated compound is heated to vaporize the U-238 but not the U-235 and separation effected; and U.S. Pat. No. 4,166,951, which is assigned to the assignee of the present invention, teaches a process wherein isotope enrichment is effected by depositing a material on a substrate, at less than a critical subatomic surface density, and selectively irradiating the deposit by a laser to excite one isotope causing the isotope to escape from the substrate, with the escaping enriched material collected.